1. Field of the Invention
The present invention relates to a photo catalyzer and discharge lamp having a photo catalytic layer.
2. Description of the Related Art
Recently, photo catalytic materials, which are activated by receiving ultraviolet rays, have been researched for various purposes.
One known photo catalytic material is titanium oxide. In particular, titanium oxide having anatase form is known to be a good catalytic material. Titanium oxide is a semiconductor having a forbidden band width of about 3.0 eV. Electron and hole mobilization occur in the titanium oxide when it absorbs ultraviolet rays having sufficient energy to cause an excited state. The energy is equivalent to a wavelength of about 410 nm. Radiation generated by conventional lamps, such as fluorescent lamps, incandescent lamps and high intensity discharge lamps include such ultraviolet rays which excite the titanium oxide. When energized, xe2x80x9cholesxe2x80x9d move on a surface of the titanium oxide. The holes attract electrons of a material in contact with the surface to oxidize it. The holes extract electrons from the material which correspond to the energy of the forbidden band width. The titanium oxide can be used as deodorizer and also used as a catalyzer to decompose a source of bad smell, such as acetaldehyde, methy-methylation-butane, hydrogen-sulfide ammonia and so on. It can also be utilized as a sterilizer in sewage disposal plants, hospitals and other places.
Japanese Laid Open Patent Application No. 1-169866 discloses a catalyzer having a layer of titanium oxide coated on the outer surface of an ultraviolet lamp. The bulb of the lamp is made of quartz glass so as to directly transmit a resonance line of mercury at 254 nm plus small additions of other ultraviolet lines such as 185 nm. The titanium oxide layer coated on the lamp operates as a photo catalyzer due to a catalytic reaction that occurs when the titanium oxide layer receives ultraviolet radiation emitted by the lamp.
Similarly, Japanese Laid Open Patent Application No. 6-304480 discloses a lamp for decomposing ethylene. The lamp is coated with a titanium oxide layer of 2 microns thickness or more.
Japanese Laid Open Patent Application No. 6-278241 discloses plate glass using for a pane. The glass plate is coated metal oxide material of several microns thickness so that the glass plate occurs a catalytic reaction when it transmits solar lays.
Japanese Laid Open Patent Application No. 7-111104 discloses a lighting fixture having a light-transparent cover coated metal oxide thereon.
However, in those prior arts, ultraviolet rays are almost all absorbed during the ultraviolet rays transmission through the titanium oxide layer. Therefore, the amount of ultraviolet rays reaching the outer surface of titanium oxide layer becomes low. As a result, it is not able to oxidize materials attached on the outer surface thereof, because there are little holes around the outer surface. Furthermore, as the transmission factor within visible light range is reduced based on the titanium oxide layer, the amount of light which transmits through the layer is reduced. Therefore, the luminous flux transmitted or radiated through the plate glass, the lighting fixture or the lamp becomes lower.
Accordingly, a primary object of the present invention is to provide a catalyzer that provides sufficient oxidation of materials in contact with a surface of the catalyzer while still providing a sufficient transmission factor.
A photo catalyzer according to the present invention has a light-transmitting substrate. A catalytic layer is provided on the substrate. The catalytic layer substantially includes anatase form of titanium oxide and has thickness of 0.01 to 0.3 microns.
Second, the present invention provides a photo catalytic apparatus including the photo catalyzer described above and a light source radiating ultraviolet radiation having a wavelength below 410 nm. The light source is provided on the other side of the substrate from the catalyzing material.
Third, the invention provides a light source having a light-transmitting envelope, means for radiating light including ultraviolet rays and a photo catalytic layer coated on an outer surface of the envelope.
Fourth, the present invention provides a lighting fixture including the light source described above and a luminaire housing the light source.
The present invention also provides a lighting apparatus including the lighting fixture described above and an operating circuit supplying electric power to the light source.
Various embodiments of the invention will be described in detail with reference to the following drawings.